The present invention relates to the field of radar imaging methods. More specifically, the present invention relates to a system and method for radar image rendering.
Enhanced vision systems are vital in the control of aircraft, especially during take off approach, and landing in adverse conditions. Radar and Electro-Optical Infra-Red (EO/IR) systems are frequently relied upon to provide these capabilities. The effectiveness of these systems greatly depends on the quality of their imaging technology.
Imaging techniques are well known and widely used in the art. Certain imaging technologies are better suited for certain applications. For example, radar imagery is widely used for navigation, surveillance, and reconnaissance, as well as target tracking and identification.
Radar imagery is conventionally accomplished by a two-dimensional scan (range and azimuth). An image is rendered from the amplitude of the reflected signals from each resolution cell (azimuth beam width, or step by range resolution length or range step) by assuming all returns are from a flat plane, which allows transforming from range/azimuth coordinates into a level X, Y Cartesian frame. The resulting image is a plan view with image intensity, grey scale shading, color or some combination thereof, in each basic resolution cell related to the radar return level. These images created from a top down perspective are useful in many applications, but suffer from several shortcomings when a view from a different perspective is required, such as, for example, from a pilot's perspective.
Conventional radar imaging systems do not provide all three coordinate dimensions (there is no elevation angle measurement) of the location of the basic resolution cell to enable the transformation of data (i.e., the image) to another perspective. Thus, they do not present objects at the proper height in the image, from the pilot's perspective.
Some of the current state of the art radar image rendering systems use databases for vertical information. In such systems, the radar sensor location is determined by a precise navigation system, and the two-dimensional image generated, as described above, is registered in absolute coordinates, enabling the use of height data from the database. This approach suffers primarily in two respects: First, there is no capability of detecting objects with a vertical dimension not stored in the database, such as construction towers erected since the database was last updated. Second, the required resolution for some applications is not available, such as is the case when a helicopter is landing in a dust cloud or fog, where a resolution on the order of one foot (30 cm) is required to assure the pilot's situational awareness.
Another shortcoming in the current state of the art in radar imaging is the irregular amplitude of returns from visually uniform surfaces due to a phenomenon known as “specular reflection.” Radar imagery traditionally employs relatively long wavelengths of reflected energy (no radiated waves), causing unnatural bright and dim areas in an image of a surface that would appear uniform to the human eye. Since the human eye is accustomed to receiving both radiated and reflected energy from detected surfaces, the reconstructed radar image seems unnatural.
The current state of the art in radar imaging is unable to provide angular resolution comparable with EO/IR sensors. This lack of resolution causes a very grainy image in the azimuth dimension, which, when coupled with the specular reflection characteristics, makes human interpretation of most radar images difficult.
There is thus a need in the art for an improved system or method to provide images with better resolution, and to present them from a pilot's perspective rather than the radar location.